1. Field Of The Invention
This invention relates to a hydraulic cylinder for a physical exercise equipment, more particularly to a hydraulic cylinder which has an improved end sleeve that provides a simple and secure connection between the improved end sleeve and the cylinder body.
2. Description Of The Related Art
Presently, there are many types of physical exercise equipments that are provided with at least one hydraulic cylinder. As illustrated in FIG. 1, a stepper (A) includes a base frame (A1); two pedal units (A2) mounted pivotally on the base frame (A1) so as to move between an upper limit and a lower limit; two conventional hydraulic cylinders (A3), each of which is connected pivotally to the base frame (A1) at one end and is connected pivotally to one pedal unit (A2) at the other end; and a reciprocating assembly (A4) attached to the base frame (A1) and having two reciprocating cranks (A5) which abut respectively against the pedal units (A2) in such a manner that when one of the pedal units (A2) is depressed so as to move to the lower limit, the other one of the pedal units (A2) is moved to the lower limit. The hydraulic cylinders (A3) provide a resistance against the pedal units (A2) when the pedal units (A2) are depressed.
Referring to FIGS. 2 and 3, the above-described conventional hydraulic cylinder (A3) includes a cylinder body (B) which has a hollow rivet bar (B1) that projects axially outward from an end of the cylinder body (B); a piston rod (C) which extends outward from the other end of the cylinder body (B) that is away from the hollow rivet bar (B1), said piston rod (C) having a hollow rivet bar (C1) projecting axially outward from the outer end thereof; and two coupling units (D) mounted respectively on the rivet bars (B1,C1). One of the coupling units (D) has a cylindrical end sleeve (D1) with two open ends. The end sleeve (D1) has a pair of diametrically opposite radial holes (D2,D3) formed in the curved side surface thereof. The hole (D3) has a diameter that is greater than that of the hole (D2) and permits the extension of the hollow rivet bar (C1) of the piston rod (C) therethrough. A rivet beater (not shown) extends through the hole (D3) so as to beat the hollow rivet bar (C1) of the piston rod (C), thereby retaining the end sleeve (D1) on the piston rod (C). The coupling unit (D) further includes two tubular pivot joint rubber cushions (D4,D5) which are pressed to fit in the open ends of the end sleeve (D1), respectively. Each of the two rubber cushions (D4,D5) has an axial bore (D6,D7) thereby permitting a pivot pin (not shown) of a physical exercise equipment (such as the stepper shown in FIG. 1) to extend therethrough. Since the two coupling units (D) have the same structure, the other one of the coupling units (D) is retained on the cylinder body (B) by connecting the corresponding end sleeve (D1) with the rivet bar (B1) so that the hydraulic cylinder (A3) can be connected pivotally to the base frame (A1) of the stepper (A) at one end and to one pedal unit (A2) at the other end, as illustrated in FIG. 1.
The main drawback of the above-described conventional hydraulic cylinder is that the hole (D3) is too small for a beater to extend therethrough so as to beat the hollow rivet bar (C1) of the piston rod (C), thereby causing undesired deformation of the piston rod (C).